For some time, mine roof bolts have been used with a mechanical anchoring device and resin grout to provide both a mechanical anchoring and chemical bonding with a mine roof bore. A stopper washer has been located on the mine roof bolt with an inner diameter of the stopper washer about equal to the diameter of the bolt and an outer diameter of the stopper washer substantially equal to the diameter of the mine roof bore so that the stopper washer stops the flow of resin down the bolt. These washers confine the resin and produce a dense resin column along a length of the bolt between the top of the mine roof bore and the stopper washer.
Examples of the use of stopper washers are disclosed in U.S. Pat. No. 4,419,805 to Calandra, Jr., and U.S. Pat. No. 4,865,489 to Stankus et al.
In U.S. Pat. No. 4,419,805 to Calandra, Jr., a metal washer is described as being retained on a bolt to effectively retain the volume of a resin mixture above the washer in surrounding relation with the bolt and its mechanical locking assembly. The washer is either welded or press fit on the bolt and spaced a preselected distance below the bolt threaded portion. In another embodiment, the washer is fabricated of an elastomeric material which is retained in gripping engagement on the bolt below the threaded end portion to retain resin mixture above the washer.
In U.S. Pat. No. 4,865,489 to Stankus et al., an adjustably securable annular washer is mounted on a shaft of a mine roof bolt. The annular washer is fixed in a position so that when a resin capsule is ruptured to release resin to bind the roof bolt within a bore hole, the resin completely fills the bore hole from the blind end of the bore to the rigid annular washer fixed to the shaft of the roof bolt. The annular washer is axially adjustable so that the roof bolt may be utilized with varying amounts of resins while still causing the resin to be subjected to a compressive force within the bore hole and in the space between the end of the bore hole and the annular washer.
A problem associated with the use of a stopper washer mounted on a mine roof bolt is that it is difficult to obtain a flat washer of the proper inner and outer diameters. The stopper washer must have an inner diameter about equal to the diameter of the bolt and an outer diameter substantially equal to the diameter of the mine roof bore. These stopper washers have to be specially made for use with a specific mine roof bolt used with a specific diameter mine roof bore. Also, the stopper washer does not assist in retaining the bolt in the bore hole.